feat: keep consistent for first

[zh-lx]

close #278

目前 first 在 pattern: 'first' 和 type: 'all' 中表现不一致：

• pattern: 'first' 中无论是否中文，都返回结果第一个字符
• type: 'all': 是中文则返回结果第一个字符，非中文返回空字符串

修改为： 是中文则返回结果第一个字符，非中文返回非中文字符串

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (f9ac8a6) to head (5179bc1).
Report is 10 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff            @@
##              main      #279   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           25        25           
  Lines        26174     26181    +7     
  Branches       503       504    +1     
=========================================
+ Hits         26174     26181    +7     

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